No bridge or building lasts forever, and gradual deterioration is inevitable; movement of cracks in concrete beams, decks, masonry walls or columns, displacement between steel framing members, or small movements in expansion joints will occur in such structures. These movements or displacements may be very slight, but they are indicators of stresses placed on such structures and they can be of vital importance in determining the continued integrity of such structures.
Current solutions consist of monitoring these types of movements and displacements in an attempt to repair or otherwise address them before they grow or present further issues. One such monitoring device is taught in U.S. Pat. No. 9,109,883 to Ansari et al, issued Aug. 18, 2015. Ansari teaches use of an arched member whose ends are respectively attached to the fixed reference frame and moving frame of the structure, the two frames separated by a gap or crack, with a strain gauge attached to said arched member; wherein a gap or crack increasing in size along an axis parallel to the line passing through the attachment points of said arch causes spreading and flattening of said arch, and through prior calibration of the arched member and strain gauge combination the amount of such movement may be reliably measured. However, if relative movements between the fixed reference frame and the moving frame occur in any other axis, such movements will twist or otherwise distort the arched member in a manner inconsistent with that in which it was calibrated, and although movements will be indicated by the strain gauge, the measurements will be erroneous. At one given location in a structure, under real-world conditions, movements of interest between the fixed reference frame and moving frame of the structure may occur in more than one axis. An assembly consisting of multiple arched members arranged orthogonally to each other might be used in an effort to discriminate between and measure movements in multiple axes at one location, but any movements in an axis parallel to a line passing through the attachment points for one arched member still will cause twisting or distortion of the other arched members in the assembly and will result in measurements that are invalid in those other arched members. Therefore, absent prior knowledge of the axis in which movement is occurring, the overall measurement can become ambiguous even with an assembly of multiple arched members arranged orthogonally to each other. Further, if relative movements between the fixed reference frame and the moving frame occur along some axis not parallel with any of the lines passing through the attachment points of any of the arched members in the assembly, the actual axis of movement cannot be determined on the basis of the strain gauge data.
Instrumentation is needed that provides highly accurate and continuous monitoring and measurement of such movements, while being rugged and robust for installation and unattended use in harsh environments over the long term. Further needed, the instrumentation should be able to determine in which axis the movement or displacement is occurring. Such instrumentation will give insights into structural health, help determine safe load limits, will help enable timely and informed application of maintenance resources needed to maintain, preserve and/or extend structure performance, and ultimately will help improve the safety, longevity and reliability of such assets.
In addition to application in bridges and buildings, such instrumentation also would have applications including and not limited to measuring the physical alignment of components, such as in machinery.